1. Field of the Invention
This invention relates generally to the field of computer graphics and, more particularly, to a high performance graphics system which implements super-sampling.
2. Description of the Related Art
A computer system typically relies upon its graphics system for producing visual output on a computer screen or display device. Early graphics systems were only responsible for taking what the processor produced as output and displaying that output on the screen. In essence, they acted as simple translators or interfaces. Modern graphics systems, however, incorporate graphics processors with a great deal of processing power. They now act more like coprocessors rather than simple translators. This change is due to the recent increase in both the complexity and amount of data being sent to the display device. For example, modern computer displays have many more pixels, greater color depth, and are able to display images that are more complex with higher refresh rates than earlier models. Similarly, the images displayed are now more complex and may involve advanced techniques such as anti-aliasing and texture mapping.
Since graphics systems typically perform only a limited set of functions, they may be customized and therefore far more efficient at graphics operations than the computer's general-purpose central processor. Graphics system processors are specialized for computing graphical transformations, so they tend to achieve better results than the general-purpose CPU used by the computer system. In addition, they free up the computer's CPU to execute other commands while the graphics system is handling graphics computations. The popularity of graphical applications, and especially multimedia applications, has made high performance graphics systems a common feature of computer systems. Most computer manufacturers now bundle a high performance graphics system with their computer systems.
Early graphics systems were limited to performing two-dimensional (2D) graphics. Their functionality has since increased to support three-dimensional (3D) wire-frame graphics, 3D solids, and now includes support for three-dimensional (3D) graphics with textures and special effects such as advanced shading, fogging, alpha-blending, and specular highlighting.
While the number of pixels is an important factor in determining graphics system performance, another factor of equal import is the quality of the image. Various methods are used to improve the quality of images, such as anti-aliasing, alpha blending, and fogging. While various techniques may be used to improve the appearance of computer graphics images, they also have certain limitations. In particular, they may introduce their own image aberrations or artifacts, and are typically limited by the density of pixels displayed on the display device.
To obtain images that are more realistic, some graphics systems have implemented super-sampling by generating more than one sample per pixel. By calculating more samples than pixels (i.e., super-sampling), a more detailed image is calculated than can be displayed on the display device. For example, a graphics system may calculate a plurality of samples for each pixel to be output to the display device. After the samples are calculated, they are then combined, convolved, or filtered to form the pixels that are stored in the frame buffer and then conveyed to the display device. Using pixels formed in this manner may create a more realistic final image because overly abrupt changes in the image may be smoothed by the filtering process.
As used herein, the term “sample” refers to calculated information that indicates the color of the sample and possibly other information, such as depth (z), transparency, etc., of a particular point on an object or image. For example, a sample may comprise the following component values: a red value, a green value, a blue value, a z value, and an alpha value (e.g., representing the transparency of the sample).
As a result, a graphics system is desired which is capable of improved performance levels to increase not only the number of pixels rendered, but also the quality of the image rendered. In addition, a graphics system is desired which is capable of utilizing increases in processing power to improve graphics effects.
Please refer to Volume I of “Principles of Digital Image Synthesis” by Andrew S. Glassner, pages 437-440, ©1995 by Morgan Kaufman Publishers, Inc., for description of a methodology for avoiding periodicity in a sampling pattern.